Polyesters and their preparation are well known in the art. Terminated polyesters, i.e. polyesters having a high proportion of non-reactive end groups, are ordinarily prepared by the reaction of a dicarboxylic acid with a glycol and a monocarboxylic acid or monohydric alcohol. Non-terminated polyesters are ordinarily prepared by the reaction of a dicarboxylic acid with a glycol.
Polyesters have found many uses in industry, among them being their use as plasticizers for vinyl halide polymers. In certain applications, polyesters are superior to monomer plasticizers since the polyesters tend to volatilize less easily and are usually less extractable by solvents, particularly in film-forming polymer systems. As the needs of industry become more and more stringent regarding the plasticization of polymer systems, it has become apparent that many polyester plasticizers must be improved in order to increase their volatility and extractability permanence characteristics.
A variety of methods are known whereby polyesters have been modified to improve their characteristics. One such method has been by the use of monofunctional reagents, e.g., acetic anhydride, to "cap" the reactive hydroxyl groups by acetylation. Such method, however, terminates the chain growth of the polyester, even though improving the extraction and volatility characteristics thereof.
Another method has been the reaction of polyesters with coupling agents, e.g. diisocyanates, which react with the hydroxyl groups present in non-terminated polyesters. The treatment of terminated polyesters with coupling agents has not been previously considered, however, since it was believed that there was an insufficient concentration of reactive hydroxyl radicals in such polyesters to react to any great extent with the coupling agent.
It has now been discovered, however, that terminated polyesters contain species of polyester which are only partially terminated and other species which are essentially non-terminated and that coupling agents will react therewith to provide polyesters of improved plasticizer performance in vinyl halide polymers.